After running EXPLAIN ANALYZE, you notice the output shows Buffers: shared hit=100 but your query is slower than expected. What might be the issue?

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PostgreSQL - Set Operations and Advanced Queries

After running EXPLAIN ANALYZE, you notice the output shows Buffers: shared hit=100 but your query is slower than expected. What might be the issue?

AThe EXPLAIN ANALYZE command was run incorrectly

BThe query plan is missing an index scan

CThe query did not run because buffers hit means error

DThe data was read from cache, so disk I/O is not the bottleneck

Step-by-Step Solution

Solution:

Step 1: Understand buffer hits
Buffers shared hit means data was read from memory cache, not disk.
Step 2: Analyze performance implication
If data is cached, slow query is likely due to CPU or inefficient plan, not disk I/O.
Final Answer:
The data was read from cache, so disk I/O is not the bottleneck -> Option D
Quick Check:
Buffers hit = data cached, disk not bottleneck [OK]

Quick Trick: Buffers hit means data read from cache, not disk [OK]

Common Mistakes:

Assuming buffers hit means query error
Thinking disk I/O caused slowness despite cache
Believing EXPLAIN ANALYZE was run incorrectly

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After running EXPLAIN ANALYZE, you notice the output shows Buffers: shared hit=100 but your query is slower than expected. What might be the issue?

Step 1: Understand buffer hits

Step 2: Analyze performance implication

Final Answer:

Quick Check:

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